Studies on biosynthesis, biodegradation, and regulation mechanism γ-polyglutamic acid in Bacillus subtilis

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Among PGA operon (ywsC-ywtABC) involved in γ-polyglutamic acid biosynthesis in Bacillus subtilis, no production of PGA was observed in ΔywsC and ΔywtA strains, but ΔywtB strain producing a small amount of PGA with 100% L-Glu. However, the ΔywtB revertant produced PGA with 70 : 30 in ratio of D, L-Glu, which is same to that of the wild-type. There are two glutamate racemases, GIr and YrpC, in B. subtilis, of which the genes were disrupted in an attempt to make clear determination of D, L-glutamate in PGA. ΔywtB-ΔgIr-ΔyrpC strain produced PGA with only L-Glu as well as that of the wild type. These results, together with the fact that the purified YwsC is able to biosynthesizes ^<14>C-PGA only from ^<14>C-L-glutamate under presence of ATP and Mg^<2+>, suggest that YwtB should possess the activity of glutamate racemase for producing PGA heterogeneous with D, L-glutamate.The structure of γ-polyglutamate-hydrolyzed product (F2) having about 2 kDa in molecular mass with D-glutamate and L-glutamate in an 80 : 20 ratio released by YwtD of B. subtilis was analyzed using γ-glutamyltranspeptidase, rat γ-glutamyl hydrolase and carboxypeptidase G. The analysis of the digested products showed the F2 product is an optically heterogeneous polymer consisting of D-γ-glutamate and L-γ-glutamate peptide units with D-glutamate in both sides, suggesting that the YwtD should be an unique endopeptidase that cleaves γ-glutamyl bond between D-and D-glutamate recognizing adjacent L-glutamate in the N-terminal side.